master broken for default Ubuntu 20.04

[Thomas Morley]

Hi,

after recent system-upgrade to Ubuntu 20.04 'make' fails on current master with

[...]
Making lily/out/lilypond
Making lily/out/lilypond.1 (help2man)
Making mf/out/mf2pt1.mem < mp
Copying mf/out/00-lilypond-fonts.conf
Copying mf/out/99-lilypond-fonts.conf
Making mf/out/fonts.conf
Making mf/out/feta-noteheads11.pfb < mf
Making mf/out/feta11.pfb < mf
Making mf/out/feta-flags11.pfb < mf
/home/hermann/lilypond-git/mf/invoke-mf2pt1.sh: 25:
/home/hermann/lilypond-git/mf/invoke-mf2pt1.sh: 25: python: not
found/home/hermann/lilypond-git/mf/invoke-mf2pt1.sh: 25:
python: not found
python: not found
make[1]: *** [/home/hermann/lilypond-git/build/.././mf/GNUmakefile:37:
out/feta11.log] Error 127
make[1]: *** Waiting for unfinished jobs....
make[1]: *** [/home/hermann/lilypond-git/build/.././mf/GNUmakefile:37:
out/feta-noteheads11.log] Error 127
make[1]: *** [/home/hermann/lilypond-git/build/.././mf/GNUmakefile:37:
out/feta-flags11.log] Error 127
make: *** 
[/home/hermann/lilypond-git/build/../stepmake/stepmake/generic-targets.make:6:
all] Error 2

python: not found
really?

I then looked for 'python'

~$ python

Command 'python' not found, did you mean:

  command 'python3' from deb python3
  command 'python' from deb python-is-python3

Just guessing, did Ubuntu 20.04 drop 'python' without a link to
'python3'? Do we need to provide aliases python = python3 or the like?
Anyway, I then installed python-is-python3 and 'make' succeeded.

I don't understand why this is not the default on Ubuntu 20.04
Though, we should take care of it, imho.

Cheers,
  Harm